Sometime in coming weeks, in one of the grand spectacles in all of nature, an insect called the periodical cicada will appear by the millions in much of central Connecticut after spending the past 17 years underground.

"It is amazing to see millions and millions and millions of cicadas all in one place," said Chris Simon, a professor in the department of Ecology and Evolutionary Biology at the University of Connecticut and a leading cicada researcher. "People are always amazed. They're underground growing, then all of a sudden one morning there will be cicadas all over tree trunks, car tires, the sides of the house, shrubbery, telephone poles, basically any vertical objects."

From East Haven east to Madison and Killingworth and north to at least Farmington, the cicadas will emerge in late May or the first week of June, climb to the tops of trees and then, a few days later, the males, seeking a mate, sing. After mating, the females cut tiny slits in small tree branches and lay their eggs. The adults live for only two to three weeks. In late summer the eggs hatch and the nymphs burrow into the ground to begin a new 17-year cycle.

Many thousands or even millions of adult cicadas in a neighborhood can produce a clamor that is unmistakable and, for some people, a big annoyance. Although they might be loud and the females can damage pencil-thick limbs on trees when they lay their eggs, the cicadas are harmless to humans; they don't bite and they are not poisonous. Rather than annoyed, many people are charmed, fascinated and awe-struck by the phenomenon.

Adult periodical cicadas are about 1 1/2 inches long, with red eyes and orange wing veins with a black "w" near the tips of the forewings. They live almost all of their lives in the ground, feeding on the fluid in tree roots and growing ever so slowly. They are a creature found only in the eastern half of the United States, and even there, spotty in their distribution. Connecticut cicadas emerge every 17 years — 1996 was the last appearance — while others, mostly in the South, emerge every 13 years.

Because of their extraordinarily drawn-out life cycle and massive numbers, periodical cicadas have fascinated scientists for decades. The researchers believe that their long life-cycle and massive numbers are a survival strategy. By appearing infrequently, predators cannot count on them as a regular food source. Also, by appearing all at once in massive numbers, predators — birds especially — cannot possibly eat them all, ensuring that some cicadas will mate and guaranteeing the survival of the species.

The latest emergence is another opportunity for researchers to learn more, and better document what is believed to be a long, slow decline in their numbers.

In fact, not only does Connecticut have 17-year cicadas, it is a virtual epicenter of cicada research, with nationally prominent researchers at the University of Connecticut and the Connecticut Agricultural Experiment Station in New Haven.

Development in which the soil is deeply disturbed is blamed for the significant if not well-documented reduction in periodical cicada territory. Cicadas are classified by their brood, a brood being a concentration of cicadas that appears in a certain 13- or 17-year cycle — including a brood once found in Connecticut that has since become extinct. The last known population in that brood, in Willington, has not been seen since 1954. That brood once stretched from Suffield south to Glastonbury and east into Rhode Island and Massachusetts.

In the remaining cicada habitat in Connecticut, populations have become ever more patchy through the decades. The scientists are planning a major effort this spring to better pinpoint exactly where the cicadas still can be found, and possibly identify some places where they exist but so far have escaped documentation.

Chris T. Maier, an entomologist at the experiment station who has studied cicadas for decades, is among the researchers monitoring this year's emergence. In 1979 and 1996, the two most recent cicada years in Connecticut, the numbers of cicadas in Farmington, for example, appeared to be tiny. Only one singing male was recorded in 1996. Farmington will be watched closely this year.

At the same time, historical records suggest that Avon, West Hartford, Rocky Hill, Newington and New Haven might still have cicadas today. Maier and a small group of researchers hope to identify any cicada pockets in those towns, and better identify pockets of cicadas in those cities and towns where they consistently have appeared. In the latest emergence, Maier also will study which predators and parasites feed on cicada eggs.

John R. Cooley, another researcher at UConn, said that technological advances in the past 17 years should make it much easier to document exactly where cicadas continue to exist. GPS, or Global Positioning Systems, for example, are far more sophisticated today, allowing researchers to pinpoint locations easily and precisely. Moreover, with the Internet now widely used, an individual who spots cicadas can post the location on a reporting website, or send an email, and researchers will be able to confirm the sighting while the cicadas are still active. In the past, sightings were reported by postcard, for example, and by the time researchers received the card, the cicadas were gone and their presence could not be confirmed.

"Anything that speeds up the flow of information helps us figure out what the distribution of the cicadas really is," Cooley said.

Simon has nearly 40 years of cicada specimens in her laboratory freezer. Working with cicada DNA, she, Cooley and associates have traced periodical cicadas to a common ancestor 4 million years ago.

Although female cicadas can kill some small tree limbs when they carve a cavity in a branch to lay eggs, it is not a serious problem for the vast majority of trees, Maier said. Insecticides are unnecessary in all but the rarest instances, such as when a fruit grower or a homeowner with an especially valuable tree finds massive numbers of cicadas on the property, Maier said.

An exhibition opens today and continues through Sept. 3 with live cicadas and detailed information on the biology of the insect at the Yale Peabody Museum of Natural History in New Haven.